1. Field of the Invention
This invention relates in general to interfaces for connecting AC and DC power sources to power supplies, and more particularly to voltage sensing, autoselecting power supply interfaces for use with on-board aircraft power sources and AC/DC and DC/DC power supplies for portable test equipment.
2. Description of Related Art
Nonstandardization on American and international fleets of trans-Atlantic aircraft of electrical power outlets used to provide auxiliary power presents a problem for portable test equipment that needs to utilize such onboard power. For example, the identical physical outlet is used to provide 28 VDC on a U.S. 747 model aircraft, and to provide 115 VAC at 400 Hz on a British Airways Model DC-10. This nonstandardization problem also exists with dissimilar U.S. model planes, e.g., a 757 versus a DC-10. This problem occurs time and time again when different model aircraft are compared.
Attempts to alleviate this problem, for example, by using cables labelled with specific voltages, still result in catastrophic equipment failures when, through user error, cables meant to connect a 28 VDC voltage using standard U.S. residential plugs are plugged into 115 VAC wall outlets.
It is known generally in the power supply art to provide power supplies that produce regulated outputs in response to a variety of input voltages and frequencies. See, e.g., U.S. Pat. Nos. 5,319,533 to Reynolds et al., 5,001,623 to Magid, 4,890,217 to Conway and 3,772,583 to Sahara et al. However, none of these power supplies permit AC and DC power sources to be connected to a common input. Further, these multi-voltage power supplies are relatively complex, and include no fail safe provision to prevent the wrong power source from being connected to the input terminals.